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Author: Steve Litt
To: dng
Subject: Re: [DNG] Long-term archiving versus medium fallibility
Hendrik Boom said on Mon, 1 Nov 2021 08:11:54 -0400

>Now storage media deteriorate over time.
>It is necessary to read and transfer data from old media to new from
>time to time. Yes, I know that. My present method is to keep
>everything on my server, and make regular backups.

Backup is, and always has been a problem. I've written several times on
the subject:





I've discovered that long term restorability depends on several things:

* How standard is the backup format? .tgz will be around for decades,
Fastback format became almost impossible to read after a decade.

* How standard is the backup media? I have some QIC tapes from the mid
90's that I don't even try to read. I have some CPM formatted
floppies from 1984 that I'm still trying to find a way to read.
Meanwhile, my ISO9660 CDs from the late 1990's, holding 8.3 filename
format .tgz files, are trivial to read.

* How robust is the backup media? Consumer grade tapes are probably
unreadable within a couple years. Some consumer grade tapes are
unrestorable one second after making them. Even worse are floppy
backups. My experience tells me that flash drives, even if formatted
as ext4 instead of that guaranteed data loss Windows format, go bad.
USB spinning rust hard drives have so far restored for me, but the
whole concept is scary. SSD is too expensive per GB to use for
backup. My restorability successes mostly revolve around CD and DVD
ISO 9660 holding tarballs in 8.3 format. I keep them in a rolltop box
to shelter them from light, and my house is air conditioned, and I see
no degradation so far. My results using Blu-Ray are mixed. Some still
restore, but some went bad, and I mean visibly bad where you could
see discolorations, within a couple years.

Anybody whose backups would require less than 5 DVDs, I'd recommend
DVDs with ISO9660 8.3 filename tarballs, additionally storing an md5
checksum for each tarball. I've never had an md5 file read
differently than the md5 value of the tarball, even after a decade.

If more than 5 DVDs worth, it's tougher. I use a combination of
UDF formatted Blu-Ray media and USB spinning rust hard drives.

I keep most of my backups in a bank safety deposit vault. Try to get a
box as high off the ground as you can, to prevent flood damage.



Steve Litt
Spring 2021 featured book: Troubleshooting Techniques of the Successful
Technologist http://www.troubleshooters.com/techniques